Reconstructing the Origin, Evolution, and History of Leprosy

This chapter synthesizes the skeletal evidence for leprosy documented in the previous chapter to explore the origin, evolution, and spread of leprosy. The relevance of the three epidemiological transitions to the frequency of leprosy since the transition to agriculture is also discussed. This is in tandem with extant modern and ancient leprosy genomic data. Ancient DNA evidence for the strains of the bacterium that affected people in the past is also furthering knowledge of the spread of leprosy. More work in this area is recommended, in concert with stable isotope analysis, providing information on the mobility and dietary histories of people in the past, and mitochondrial DNA to document ancestry. The historical evidence suggests that leprosy declined in the fourteenth century, but at the moment archaeological evidence is lacking to support such a hypothesis. Many reasons for this have been suggested (for example the plague, and improved diet and living conditions), but cross-immunity created by exposure to tuberculosis remains the strongest possibility. The two diseases have many characteristics in common, and tuberculosis and leprosy have been found together in skeletons in a number of instances. Co-infection with tuberculosis may be another hypothesis to consider as an explanation for leprosy’s decline.